Noun. When a group of kids put their underpants on their heads and run around yelling.
Less commonly, when a group of men who've been drinking do the same thing.
On 30 January a bunch of guys checked in beers while wearing their undies on their heads. They claimed it was a Machuchu Party.
A party where a females underwear is worn on ones head for the sole purpose of drinking beer through them.
He wore frilly silk knickers on his head for the Machuchu party.